MECHANISM OF THE OSSICLES OF THE EAR. 753 



focus as they impinge upon the retina ; but as far as the action of the acces- 

 sory parts of the ear are concerned, the waves of sound are unaltered ; that 

 is, the rate of their succession remains absolutely the same, though they be 

 reflected by the concavities of the concha and repeated by the tympanic 

 membrane. Even if it be assumed that the membrane under normal condi- 

 tions repeats musical sounds by vibrations produced by influence, and that 

 sounds are exactly repeated, the position of these sounds in the musical scale 

 is not and can not be altered by the action of any of the accessory organs of 

 hearing. The fact that a person may retain his musical ear with both mem- 

 branes destroyed is not really an argument against the view that the mem- 

 brane repeats sounds by influence ; for if musical sounds or noisy vibrations 

 be conducted to the auditory nerves, the impression produced must of neces- 

 sity be dependent exclusively upon the character, regularity and number of 

 the sonorous vibrations. And, again, the physical laws of sound teach that 

 a membrane, like the membrana tympani, must reproduce sounds with which 

 it is more or less in unison much more perfectly than discordant or irregular 

 vibrations. In a loud confusion of noisy sounds, one can readily distinguish 

 melody or harmony, even when the vibrations of the latter are comparatively 

 feeble. 



It has been shown that the appreciation of the pitch of sounds bears a 

 certain relation to the degree of tension of the tympanic membrane. When 

 the membrane is rendered tense, there is insensibility to low notes. When 

 the membrane is brought to the highest degree of tension by voluntary con- 

 traction of the tensor tympani, the limit of appreciation of high notes may 

 be raised from three thousand to five thousand vibrations. It is a fact in the 

 physics of the membrana tympani that the vibrations are more intense the 

 nearer the membrane approaches to a vertical position ; and it has been ob- 

 served that the membrane has a position more nearly vertical in musicians 

 than in persons with an imperfect musical ear (Troltsch). 



Experiments have shown that the tympanic membrane vibrates more 

 forcibly when relaxed than when it is tense. In certain cases of facial palsy, 

 in which it is probable that the branch of the facial going to the tensor tym- 

 pani was affected, the ear has been found painfully sensitive to powerful im- 

 pressions of sound. This probably has no relation to pitch, and most sounds 

 that are painfully loud are comparatively grave. Artillerists are in danger of 

 rupture of the membrana tympani from sudden concussions. To guard 

 against this injury, it is recommended to stop the ear, draw the shoulder up 

 against the ear most in danger, and particularly to inflate the middle ear 

 after Valsalva's method. " This method consists in making a powerful ex- 

 piration, with the mouth and nostrils closed " (Troltsch). 



Mechanism of the Ossicles of the Ear. The ossicles of the middle ear, in 

 connection with the muscles, have a twofold office : First, by the action of 

 the muscles the membrana tympani may be brought to different degrees of 

 tension. Second, the angular chain of bones serves to conduct sonorous 

 vibrations to the labyrinth. It must be remembered that the handle of the 

 malleus is closely attached to the membrana tympani, especially near its 



